A Long Term Evolution (LTE) network consists of an evolved Universal Terrestrial Radio Access Network (E-UTRAN) and an Evolved Packet Core (EPC) and is of a flat structure, wherein the E-UTRAN can consist of a plurality of evolved base stations (i.e. evolved NodeB, eNB) connected with the EPC.
In the LTE system, if needing to interact with the network side, a UE needs to acquire uplink synchronization firstly and initiate a random access procedure. The random access procedure can be classified into competition-based random access procedure and non-competition-based random access procedure according to the mode.
FIG. 1 shows a flowchart illustrating the competition-based random access procedure, and as shown in FIG. 1, the competition-based random access procedure mainly comprises the following steps:
S101: a UE transmits a random access preamble on an uplink random access channel, wherein the time-frequency domain location for transmitting the preamble is associated with a Random Access Radio Network Temporary Identifier (RA-RNTI);
S103: after receiving the random access preamble, an eNB replies a random access response to the UE on a downlink shared channel, wherein the random access response comprises authorization for subsequent uplink scheduling of the UE by the eNB;
S105: if the UE identifies a response associated with the preamble transmitted in S101 on a downlink control channel according to the RA-RNTI, the UE performs the uplink scheduling according to the authorization obtained from the eNB in S103 and transmits an Msg3 to the eNB, wherein the Msg3 includes a UE identifier or a contention resolution identifier; a HARQ (Hybrid Automatic Repeat Request) repeat mechanism can be adopted in the process, i.e., if the eNB replies that the message has not been received (i.e. negative acknowledgement, NACK), the UE retransmits the Msg3; and
S107: after receiving the Msg3, the eNB transmits an Msg4 to the UE according to the UE identifier; if the UE receives the message before a contention resolution timer is timeout and determines the Msg4 to be the Msg4 expected by the UE through unpacking, the UE determines that the random access procedure is successful; otherwise, the random access procedure is determined to be unsuccessful and a random access is reinitiated.
FIG. 2 shows a flowchart illustrating the non-competition-based random access procedure, and as shown in FIG. 2, the non-competition-based random access procedure mainly comprises the following steps (step S201-step S205):
S201: the eNB allocates a dedicated random access preamble for the UE through a dedicated signaling firstly, wherein, in the preamble, a time-frequency domain location for transmitting the random access is designated;
S203: the UE transmits the dedicated random access preamble in the designated time-frequency domain location; and
S205: after receiving the random access preamble, the eNB replies a random access response to the UE on the downlink shared channel; if the UE identifies a response associated with the dedicated preamble transmitted in step S201 on a downlink control channel according to the RA-RNTI, the UE determines that the random access procedure is successful; otherwise, the random access procedure is determined to be unsuccessful and a random access is reinitiated.
Herein, there are 64 preamble sequence codes used for the random access in each cell, according to the competition-based and non-competition-based access mode, the preamble codes are divided into two groups; the preamble codes for the competition-based random access are further divided into two groups, Group A and Group B, according to the size of a subsequent Msg3 and the magnitude of the path loss during the measurement. Therefore, the 64 preamble codes are divided into three groups.
As it is possible that a plurality of UEs initiate the random access procedures simultaneously at a certain moment in the cell, the competition-based random access procedures using the preamble codes in the same group may lead to the occurrence of a contention phenomenon, thereby cause the failure of the random access procedure initiated by the UEs or the subsequent interaction between the UEs and the network side and finally cause a larger time delay for a call establishment and switching of partial UEs in the cell as well as a lower success rate. Furthermore, a Physical Random Access Channel (PRACH) needs to fixedly occupy partial air interface resources of the cell, so improper configuration of the PRACH will lead to waste of the radio resource of the cell. In order to solve the problem, it is possible to acquire the cell performance parameters by the field manual test method or the like after the establishment of the cell, and manually modify the corresponding configurations, so that the performance of the system is improved. However, because of the complexity of a radio environment and the time invariability of manually optimized system parameters, network optimization efficiency is low, which leads to an enormous amount of manpower costs.
At present, in order to reduce the manual maintenance workload and improve the optimization ability of the network, the Next Generation Mobile Network (NGMN) organization requires that the LTE needs to support the Self-Organized Network (SON) function, wherein the function includes a self-optimizing function of a random access channel. The parameter configuration of the cell (including the configuration of the random access channel) may be automatically optimized through the self-configuration function and self-optimizing function of the network. However, in order to optimize the network, the performance index of the current network must be acquired firstly, in the existing protocol of the LTE, the performance index is acquired by an input parameter of the random access optimization function, which is the number of times that the base station receives a Random Access Channel (RACH) preamble from the UE, and is counted by the base station.
However, the input parameter cannot reflect contention, delay, failure and other problems in the random access procedure caused by an improper PRACH configuration parameter. Therefore, the problem to be solved in the prior art is how to precisely acquire the input parameter information for the random access optimization.